Patients showing symptoms of depressive illness were treated in general practice with one of four clomipramine (Anafranil) dosage regimes (25 mg t.d.s., 75 mg o.n., 10 mg t.d.s. and 30 mg o.n.). Blood was sampled on admission to the study and at days 7, 14 and 28. Plasma analysis revealed that steady-state concentrations of clomipramine and its main metabolite desmethyclomipramine were reached at day 7 of treatment in each of the dosage groups. No apparent relationship between dosage and plasma level of clomipramine was found in this study since there was no significant difference between mean steady-state plasma levels in each of the four dosage regimes. In contrast, plasma concentrations of desmethylclomipramine appeared to be directly related to the dose of clomipramine administered. Intersubject variations in plasma levels of the parent compound within each dosage group ranged from three to fourteen-fold.